According to new research released this month, each vehicle used for one-way car sharing, in particular, can eliminate as many as 11 cars from plying the streets and cutting greenhouse gas emissions by nearly 13 metric tons a year.

The service allows people to rent a car in one location and drop it off at another, paying for the trip by the minute. This is different than two-way car sharing, which requires a driver to pick up and return a vehicle at the same spot, or peer-to-peer car sharing, which involves privately owned vehicles.

The three-year study examined the impact of the Car2go service in Seattle, San Diego, Washington DC and two Canadian cities, Calgary and Vancouver.

“One-way, free-floating car sharing is taking cars off the road and reducing mileage, as well as emissions,” said Susan Shaheen, co-director of TSRC. “This study provides a series of key metrics to aid policymakers and decision makers in understanding the possible impacts of these services on cities.”

The TSRC researchers collected data from 9,500 members of Car2go and found that most people used the service for short-distance travels that were under 5 miles on average. Yet many customers over time either sold their own cars or decided against buying new ones, even if that meant they would have to find alternatives for long trips.

Researchers estimated that the service kept 28,000 privately owned cars off the streets. They surveyed Car2go customers and found that 2%-5% of people sold their cars and 7%-10% decided against buying a vehicle. The cars sold also averaged 14 years old and ran on older and more polluting emissions systems.

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People tend to drive less when they don’t own cars, researchers found. As a result, researchers calculated that the miles avoided were greater than those created by Car2go, leading to a reduction of between 10m-29m miles annually per city. This removed, on average, between 5.5-12.7 metric tons of carbon emissions per vehicle per year.

One-way car sharing is commonly used for the so-called “first and last mile” – transport-speak for short journeys to and from public transit such as bus and train stations, said Sharon Feigon, executive director of the Shared Use Mobility Center, a nonprofit that advocates for car and bike sharing.

As a result, car sharing services can help local governments that come under increasing pressure to meet ambitious emissions targets and aim to make public transportation more accessible. “This is one more option in the toolkit of how you create good mobility in the city,” said Feigon, who previously ran a car sharing business in Chicago.

Of the five cities in the study, those with the largest public transportation and car sharing programs had the biggest impact, Feigon noted. In Seattle, for example, Car2go removed 9,000 metric tons emissions in 2015 and reduced overall vehicle miles traveled by more than 34m.

“You can see there’s a network effect in the places with the supportive policies and most coverage,” said Feigon. “Car sharing is a more useful service when you can scale it up and connect it with other modes of transportation.”